Currently, the electrical mechanical stretching device of the movable sofa in the prior art has four significant defects. 1, In the market, the structure of the electrical driving means of the movable sofa is too complex, affecting the kinetic efficiency of the motor. 2, In the market, the electrically driving means of the movable sofa causes shaking, affecting the comfortability of the movable sofa. 3, In the market, the electrical driving means of the movable sofa are difficult to install, affecting the installation efficiency of the movable sofa. 4, In the market, since the motor head of the electrical driving means of the movable sofa project outside the electrical connecting rod, interference will occur when the leg is completely folded, affecting the function of the sofa and the stability of the structure. Referring to FIG. 5, in the market, the electrical device of the electrical driving means of the movable sofa in the prior art includes electrical rectangular pipe 10, electrical angle iron 11, transmission part 12, transmission fixing support 13, comparing motor head fixing part 14 (hereinafter, the word “comparing” in the context is used to distinguish different embodiments), comparing motor connecting rod 15, motor fixing part 16, motor tail fixing part 17, comparing motor movable sliding block 18, comparing motor 19, rotating shaft transmission part 20, rotatable connecting rod 21, and comparing electrical connecting rod 9. It is necessary to fix the front end and the rear end of comparing motor 19 on comparing motor connecting rod 15 and the comparing electrical connecting rod 9, respectively. By assembling transmission part 12, the transmission fixing support 13, and the motor fixing part 16 as an electrical rotatable connecting pall, the linear movement of comparing motor movable sliding block 18 on comparing motor 19 is transformed into the rotating movement of electrical rectangular pipe 10 and the electrical angle iron 11, such that rotating shaft transmission part 20 and rotatable connecting rod 21 that are connected to electrical rectangular pipe 10 are driven to rotate, and thus the mechanical stretching device is driven to move. Since self-locking of the iron frame may happen during the rotation of rotating shaft transmission part 20 and rotatable connecting rod 21, the problem that the electrical driving mechanism will cause shaking is raised. The present invention makes improvements based on the above prior art.